1. Field of the Invention
The invention relates to a method for continuous measurement of the dynamic fluid consumption of a consumer by means of a two-way flow sensor, particularly the measurement of gaseous or liquid fuel, and possibly a conditioning device, whereby the pressure is reduced to a constant exit pressure downstream from the flow sensor. The invention also relates to a device to carry out the method comprising a continuously operating flow sensor, a pressure regulator as well as a pump and possibly at least one conditioning device on the exiting side.
2. The Prior Art
Either a combination of a measuring device and a conditioning device is used for measurement of the consumption of fluids, especially in the use of measuring fuel consumption of engines on test benches—or the object is achieved through an integrated system. The object of these systems is to provide defined and reproducible conditioning of the physical fluid characteristics at the intersection to the test piece. This means, the pressure and the temperature is set at least to adjustable constant values.
Intermittently operating systems using weighing devices are known in the art for taking measurements. They have the advantage of open systems, namely the characteristic whereby fuel can be delivered from the measuring system and it can also be returned at intervals into the system limited by the feeding volume. The delivered quantity of fuel as well as the returned quantity of fuel is measured and it is included in the consumption data. Open systems are advantageous especially in modern injection systems since they push fuel back into the fuel supply system within limits—into the tank in case of a vehicle—at starting of the engine and during the pressure build-up in the injection system. Weighing devices have been shown to be of disadvantage in that they have to be refilled repeatedly and a continuous measuring operation is thereby not possible.
Measuring devices are often used for continuous measurement of fluid consumption performing volumetric measurements or for measuring the flow rate. The consumed fuel mass is thereby determined by means of an additional density measurement which then represent the actual necessary measured variable. Direct measurement of consumption of mass is currently possible by means of traditional commercial Coriolis sensors.
Attention has to be paid in taking accurate measurement during employment of these sensors that no multiphase flow occurs in any operational condition, which means, even in case of dynamic changes of the consumer. This may occur, above all, during operation using gasoline while falling below a minimum pressure locally. A greatly higher pressure is created therefore upstream from the sensor than needed directly at the intersection to the test piece.
Various methods and devices are known in the art for conditioning of the pressure. For example, a pressure stabilization device to stabilize the inlet pressure of the mass flow sensor is provided in AT-3.350 U to be able to produce the required low and constant pressure at the connection to the consumer (generally in the range of a few millibars). The flow-dependent pressure drop must therefore be variably compensated on the mass flow sensor in the use of a Coriolis sensor (by up to 2 bars, for example). In particular, high-frequency, spiking or pulse-like drawing of fluid must be quickly taken into consideration.
A pressure control device (pressure regulator) is therefore provided downstream from the actual flow sensor for pressure stabilization in the above-mentioned continuous method of fuel measurement which adjusts the flow-dependent pressure at the exit of the measuring system to a constant exit pressure. It is of a disadvantage in such a design that conventional mechanical pressure regulators act as a “hydraulic diode”, whereby it is meant that flowing medium can flow only in one direction, namely downstream. A measuring system designed with such a pressure regulator does not represent an open system. Should fuel have to be returned from the injection system into the measuring system or should there occur thermal expansion of the fuel through a rise in temperature during a halt in operation by the consumer, then there is mostly created an unacceptably high pressure increase within the fuel system, depending on the elasticity of the pipe system, which stresses lines and connected devices whereby the high pressure must be caught by costly pressure compensation devices, if necessary.
AT-6303 U disclosed a solution which has the disadvantage that no open system has been created which would make a return flow through the flow sensor possible even though fuel can be returned in a limited manner, which means, the problem of pressure increase is sufficiently solved.
AT-6117 U discloses for the first time a solution which realizes an open system with continuous consumption measurement. The problem is solved through the control of pressure upstream from the sensor in a manner so that the desired exit pressure is provided downstream from the sensor. However, the exit pressure of the system is limited by the minimal entrance pressure in front of the flow sensor. Any lower pressure than that can not be adjusted. A system is also described in U.S. Pat. No. 5,284,120 A wherein a pressure sensor if arranged behind a flow sensor whereby said pressure sensor has again a controlling effect on the devices arranged in front of the flow sensor. However, a pressure reduction valve is provided between the flow sensor and the pressure sensor to lower the exit pressure for the consumer to the atmospheric pressure in a constant manner. Disclosed is again a system in which the flowing medium can flow through the regulator only in one direction, namely downstream, which means, U.S. Pat. No. 5,284,120 A does also not represent an open system. Nevertheless, a small quantity of the fluid can be taken up by a damping unit but timely cross reference between the measured consumption on the flow sensor and the actual consumption is made thereby unclear again. The disclosed arrangement is therefore not suitable for timely, highly defined and accurate measurement of fuel consumption.
The fuel temperature delivered to the test piece is of great significance aside from the constant pressure. It is legally directed for prototype tests that the temperature of the fluid must lie constant within a defined temperature interval at the intersection to the test piece. Temperature conditioning devices are used for this purpose. They are installed in the fluid circuit mostly downstream from the flow sensor. They form either an individual conditioning circuit, which is closed by means of a so-called bypass near the test piece, or said temperature conditioning devices are disposed directly in the engine circuit. In the first case, the circulating quantity of fuel in the conditioning circuit must be kept up by means of a pump. In the second case, the conditioning circuit is identical to the engine circuit and the fluid is returned mostly by the pump used in the test. The creation of an individual conditioning circuit is more advantageous since in that case stable pressure and temperature conditions can be created at the intersection to the test piece without operation of the test piece (in this case it is the bypass).
Currently commercially obtainable fuel measuring and conditioning systems are provided thereby with a measuring circuit and an inlet circuit in front of the sensor that is mostly used for venting and uncoupling of facility fuel lines. The actual measuring element of the flow sensor is disposed between these circuits. The measuring circuit consists either of an individual conditioning circuit closed by means of a bypass and the engine circuit or it consist exclusively of the engine circuit.
The stability of the mean temperature or the stored energy of the fluid maintained in the measuring circuit is of immense significance relative to the precision of measurement since each temperature change in the volume downstream from the sensor leads to so-called false flow readings under the assumption of constant geometric conditions (caused by the mostly rigid lines) and based on the thermal expansion of the fluid whereby said false flow readings appear as false readings for the entire system.
The object of the present invention was to provide a method and a device which makes possible a continuous, accurate and timely highly defined consumption measurement with controlled exit pressure for the fluids be means of an open system, which also allows at least a temporary return flow at simultaneous flow measurement, which is able even at highly dynamic consumption changes to maintain pressures in the entire line system, and which does not allow the formation of a multiphase flow.